A diode having a PN junction (hereinafter referred to as “PN diode”) and a diode having a Schottky junction (hereinafter referred to as “Schottky diode”) are widely known as a semiconductor diode. The PN diode has characteristics of high withstand voltage during turn-off and small reverse leakage current.
In a vertical power semiconductor device, a large current flows between electrodes facing each other. Recently, in the vertical power semiconductor device, a multi RESURF structure is adopted as a technique of enhancing the withstand voltage while reducing on-resistance. The multi RESURF structure is a structure that P-type layers and N-type layers are alternately arranged.
The multi RESURF can provide a compatibility of reducing on-resistance and enhancing withstand voltage in a PiN-type diode, for example.
However, when a silicon substrate is used, a threshold of forward voltage is high because a built-in potential generated by a band gap of a PN junction is as high as about 0.8 V. At the threshold, on-current starts to flow through the PiN-type diode.
On the other hand, as to a Schottky diode, a barrier height of a Schottky electrode and a drift layer can be controlled.
Accordingly, a built-in potential of the Schottky diode, i.e. a threshold of the Schottky diode at which on-current starts to flow, can be lowered. A multi RESURF structure to be employed in a Schottky diode has been proposed.
However, leakage current increases in the Schottky diode significantly when withstand voltage is enhanced.